# Newbie: SPDT Switch explaination please

I am trying to figure out exactly what a SPDT Switch does and how it works. My 10 year old nephew and I are going to put together a Beetlebot
http://members.tripod.com/robomaniac_2001/id120.htm this weekend and I want to be able to teach him something from it all. I think it would helpful if I could explain what the SPDT switches do so that he can understand that they are the bot's brain.
Could someone please shed some light on the subject?
Many thank's, Peter
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o_o x spst
o_o x dpst o_o x
o_o o spdt
o_o o dpdt o_o o
if this is not helpful i can drawr up something more decent, and add some more grandios text.
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SPDT is an acronym for Single Pole, Double Throw.
Single pole means there is only one switch inside, as opposed to a double throw switch which acts like two switches side-by-side connected by the same knob.
Double Throw means that the switch can direct the electricity to go out from the switch through two different wires, depending on which way the switch is positioned.
Note that on the switch there are 3 pins. The electricity goes in the middle pin, and if the switch knob is in one position, the electricity will flow out the pin on the left, and if the knob is moved to the other position, the electricity will instead go out the other pin.
It is like a diverter valve for water. Note that if one side of the SPDT is not connected to anything, it simply acts like an on-off switch.
On an electronic device, even if you want the switch to act like an on-off switch, it is best for the off postion to actually connect to ground. If it weren't connected to ground, it is "floating" and can act like a tiny antenna and pick up voltages from radio transmissions and other things.
Of course, another way to find out what it is like, is to take the switch apart. But be sure to get a spare because you may not be able to get it back together.
Joe Dunfee
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On 4 Feb 2005 22:16:08 -0800, snipped-for-privacy@yahoo.com wrote:

^^^^^^ ^^^^^
Oops, you obviously mean Double Pole here.

The 'middle pin' is correct for many types of switch such as the common toggle and slide types, but I saw the diagrams for these things on the mentioned website, and the pin that gets switched between the other two is at one end, not in the middle. They are labeled:
C N.C. N.O.
These are Common, Normally Closed, Normally Open.
This is a spring-return switch used as a bumper for the bug. Without anything touching it, the C pin is connected to the NC pin. When something presses on it, the C is disconnected from the NC pin and connected to the NO pin.
To really see how switches work, you need a really big, old-fashioned knife switch, a battery, and light bulbs. :)